DiskAid is an application to transfer files from PC to iPhone or iPod Touch as if it was a common Hard Disk.
You only have to run it and then, plugin the device. The computer will detect it as removable HD and you'll be able to work as usual.
However, DiskAid is not the way to transfer music from PC to iPhone. You'll need iTunes or similar software to do that.
Take the most out of your iPhone / iPod Touch by using DskAid.